Strategy for Long-Term 

Management of Exotic 

Trees in Riparian Areas for 

New Mexico’s Five River 

Systems, 2005-2014

United States

Department of

Agriculture

Forest

Service

Southwestern

Region
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Printed on recycled paper • March 2004

This strategy was prepared by the New Mexico Interagency Weed 

Action Group (IWAG), which is an ad-hoc group of Federal and 

State resource management agency representatives and university 

research specialists involved with invasive weed management. 

First organized in 1999, IWAG members have been cooperating 

in addressing invasive weed action programs of mutual concern.
Strategy for Long-term Mgmt. of Exotic Trees in New Mexico’s Riparian Areas 1

Draft

This strategy addresses the longterm management of saltcedar 

(Tamarix spp.), Russian olive 

(Elaeagnus angustifolia), and 

Siberian elm (Ulmus pumila) in the 

narrow belts of riparian vegetation 

along the Rio Grande, Pecos, 

Canadian, San Juan, and Gila/San 

Francisco River systems, including 

connected perennial, intermittent, 

and ephemeral streams. The 

ongoing degradation of native plant 

communities in riparian areas is 

a significant concern of citizens of 

New Mexico; a concern shared by 

Federal, State, and local resource 

managers.

This is a scientifically based strategy 

that provides a broad framework for 

Integrated Vegetation Management 

(IVM) of exotic tree infestations. 

Preventing the continued spread 

of these infestations, controlling 

existing infestations, and 

maintaining and improving the 

health of native plant communities 

are the ultimate goals of this 

strategy. The various adverse 

environmental, social, and economic 

consequences associated with the 

outbreaks are significant, and they 

will continue to increase without 

direct intervention.

This long-term strategic approach is 

meant to serve as a common sense 

blueprint to assist in protection 

and restoration efforts being 

implemented by agency managers 

and private landowners, and provide 

a framework for the development of 

local plans. To be successful, agency 

managers and landowners will need 

to undertake coordinated control 

and restoration throughout the five 

river systems. Although several 

closed water basins in New Mexico 

are not addressed in this plan, the 

same management concepts can be 

applied to these basins.

Since large-scale coordinated 

programs require a substantial 

commitment of Federal and State 

funds, a higher level of assessment 

for entire river systems is needed. 

Participating agencies acknowledge 

that riparian protection and 

restoration efforts must extend 

beyond administrative boundaries, 

and local groups must be active 

participants.

Adequate, consistent, and longterm funding will need to be 

provided to achieve successful 

control of exotic tree infestations 

and restoration of riparian areas. 

To address infestations in the five 

river systems, it is estimated that 

at least $64,400,000 of Federal and 

State cost-share funding (including 

volunteer and in-kind services) 

will be needed for the first 10-year 

period under this plan. Funding 

would need to be balanced between 

prevention, treatment of light 

infestations, protection of areas of 

special concern, and large scale 

infestations.

This plan is supported by the 

Southwest Strategy and the New 

Mexico Interagency Weed Action 

Group (NMIWAG). This project was 

developed under the Memorandum 

of Understanding for Coordinated 

Resource Management (CRM), 

which provides a mechanism for 

Federal, State and local interests to 

foster communication, cooperation, 

and coordination in developing 

and implementing sound resource 

management and conservation 

programs.

Executive Summary
2 Strategy for Long-term Mgmt. of Exotic Trees in New Mexico’s Riparian Areas

Purpose

This strategy provides a broad 

framework for Integrated Vegetation 

Management (IVM) of exotic trees 

throughout the five major river 

systems in New Mexico (Figure 

1 and Table 1). It is designed to 

encourage public land managers 

and private landowners to 

undertake coordinated control and 

restoration. It identifies long-term 

objectives to address infestations 

and defines measures of success.

Strategic Plan

Figure 1. Major river systems in New Mexico 

Scope and 

Background

Saltcedar, Russian olive, and 

Siberian elm are capable of invading 

a wide range of areas throughout 

New Mexico, including riparian 

habitats, rangelands with ephemeral 

springs, roadsides, urban areas, 

and mountain meadows and 

forests. While management plans 

will need to consider all infested 

areas, this document focuses 

on riparian habitats, including 

connected perennial, intermittent, 

River Basin

Canadian

Gila/San Francisco

Pecos

Rio Grande

San Juan

0 25 50 75

Miles
Strategy for Long-term Mgmt. of Exotic Trees in New Mexico’s Riparian Areas 3

Draft

IVM is a 

structured 

approach to 

developing 

a weed 

management 

plan that 

optimizes 

management 

to meet 

specifi c 

objectives for 

the land.

Table 1. Watershed area and total stream length for fi ve river systems 

in New Mexico

Watershed Area

(square miles)

Total length of the main 

stem and tributaries

(miles)

Rio Grande 31,960 3,410

Pecos 23,810 2,760

Canadian 17,660 2,500

San Juan 9,760 1,450

Gila/San Francisco 5,400 690

and ephemeral streams, as these 

are critical to wildlife and have high 

recreational value to New Mexicans.

Climatic fluctuations, combined 

with human activities, have resulted 

in significant changes to riparian 

woodlands in New Mexico. The 

introduction of saltcedar, Russian 

olive, and Siberian elm into New 

Mexico in the early 1900s has 

resulted in profound changes in 

riparian forests and nearby areas 

(Shurlock 1987). These exotic trees 

have quickly spread along the Rio 

Grande, Pecos, and San Juan River 

systems, replacing native plant 

communities, and becoming the 

dominant species in many places. 

Infestations continue to spread 

and intensify throughout all river 

systems in the State.

While many citizens understand 

that the current vegetative 

conditions are unnatural, they value 

the rivers and the adjacent bosques 

(DeBuys 1993). Dense stands of 

exotic trees have limited recreational 

value and increased risk for 

wildfires (Stuever 1997). Also, the 

demand for water exceeds supply 

in virtually every river basin in the 

State (New Mexico Office of the 

State Engineer and the Interstate 

Stream Commission, Framework 

for Public Input to a State Water 

Plan, 2002). The recent drought has 

added emphasis to the problem of 

Figure 2. Riparian areas provide 

essential habitat for migrating birds .

excessive water use by these exotic 

tree species.

Long-term management is needed 

to address the continued spread 

of exotic weeds and associated 

adverse consequences for future 

generations of New Mexicans. Other 

invasive tree species, such as treeof-heaven (Ailanthus altissima), 

have invaded riparian areas and 

other woody species are expected to 

become established in the future. 

Management of these invaders must 

be addressed as part of any riparian 

restoration effort.
4 Strategy for Long-term Mgmt. of Exotic Trees in New Mexico’s Riparian Areas

The natural and restorable 

riparian areas are an invaluable 

resource for the State. Protection 

and improvement of these areas 

will not only enhance biological 

diversity, but will also provide 

benefits for economic stability 

and environmental quality. With 

planning and coordination, the 

highly productive plant communities 

can be managed in a cost effective 

and environmentally compatible 

manner.

In addition, other invasive weeds are 

becoming established throughout 

riparian areas in New Mexico. These 

species can invade riparian areas 

and survive underneath canopies 

of existing native and exotic trees. 

Any efforts to manage the exotic 

tree species covered in this plan 

must avoid spreading or creating 

opportunities for these species 

to thrive. Whenever possible, 

management plans should also 

address other invasive species 

existing in the understory. Russian 

knapweed (Acroptilon repens), 

perennial pepperweed (Lepidium 

latifolium), camelthorn (Alhagi 

pseudalhagi), and leafy spurge 

(Euphorbia esula L.) are of particular 

concern in New Mexico (Lee 1999).

Biology and Ecology of 

Exotic Phreatophytes

Saltcedar (Tamarisk spp.): 

Saltcedar is a deep-rooted 

deciduous shrub or tree that can 

reach up to 25 feet in height. While 

initially introduced for erosion 

control, it has escaped cultivation 

and can form dense monotypic 

stands along riparian and flood 

plain habitats and open savannalike infestations in upland areas. 

It is widely distributed throughout 

the West, and surveys estimate 

over 1.5 million acres are infested 

in the Southwest alone (Brotherson 

and Field 1987; Brock 1994). In 

New Mexico all major watersheds 

have documented infestations of 

saltcedar, with the Rio Grande, 

Pecos, Canadian, and San Juan 

River systems having large reaches 

dominated by saltcedar. Within New 

Mexico, the Gila and San Francisco 

River basins are still predominately 

comprised of native species, but the 

Figure 3. Flowering saltcedars in Pump Canyon, a tributary of the San Juan River.
Strategy for Long-term Mgmt. of Exotic Trees in New Mexico’s Riparian Areas 5

Draft

potential exists for further spread of 

exotics (Dr. Mark Renz, New Mexico 

State University, 2003, personal 

communication).

Saltcedar establishes in areas 

associated with native species such 

as screwbean mesquite (Prosopis 

pubescens), cottonwoods (Populus

spp.), and willows (Salix). Seeds 

germinate readily in moist areas 

that are frequently disturbed 

(Horton et al. 1960; Stromberg 

1997). If the correct conditions 

exist (moist soil for several weeks), 

plants can grow up to 6 to 9 feet 

in a season and produce seeds 

within the same year (Friederici 

1995). Root growth is predominantly 

downward with little branching 

until plants reach the water 

table. These characteristics allow 

saltcedar to be very competitive and 

capable of displacing resident plant 

populations (Lovich et al., 1994) 

without native plant competitors 

(Sher et al. 2002). Over time, the 

competitiveness of saltcedar has 

allowed it to form impenetrable 

thickets in many riparian areas 

where environmental stress is high 

(Brotherson and Field 1987; Sher et 

al. 2002).

Long distance spread of saltcedar 

is primarily through seed dispersal, 

but vegetative propagation is 

usually responsible for local spread 

and infestation intensification. 

Plants typically bloom from April 

through October in New Mexico, 

and a single plant is capable of 

producing up to half a million seeds 

per year (DiTomaso 1998). Seeds 

are dispersed into the environment 

by wind and water, but are viable 

for only a few weeks (Brotherson 

and Field 1987). Plants can also 

spread vegetatively by resprouting 

from roots and stems that have 

been buried (Frasier and Johnsen, 

1991). While stems rarely fragment 

naturally, some management 

techniques may lead to vegetative 

spread.

Russian olive (Elaeagnus 

angustifolia L.): This is a fast 

growing deciduous tree that can 

reach up to 40 feet in height (Brock 

1998; Whitson et al. 2000). An 

ornamental tree first introduced 

for landscaping and windbreaks 

in the late 1800s, Russian olive 

has spread and is now naturalized 

throughout the central and western 

United States. It is highly invasive 

in seasonally wet riparian and flood 

plain habitats, where it has been 

observed to replace native willow 

and cottonwood species (Crawford et 

al. 1993). It can grow under dense 

stands of saltcedar, out compete 

resident plants, and eventually 

dominate some riparian sites (Olson 

and Knopf 1986). Russian olive can 

also tolerate high salt levels in soil 

and drought (Brock 1998). Dense 

infestations are common along the 

San Juan River and northern sections 

of the Rio Grande. Note the Russian 

olive infestation along the edge of the 

Rio Grande in Figure 11.

Leaves of Russian olive are grayish 

green with silvery scales, and the 

bark is dark brown. Established trees 

are very competitive and plants can 

grow up to 5 feet per year. The root 

system grows deep into the soil with 

many well-developed lateral roots. 

Seedlings and saplings can survive 

in low light under canopies (Shafroth 

et al.1995). Plants can also tolerate 

drought conditions.

Russian olive reproduces primarily by 

seed, and seed-eating birds result in 

long distance dissemination. Plants 

flower from May through June in 

New Mexico, and seedlings germinate 

from fall through spring. Seeds 

can survive 3 years in controlled 

conditions (Schopmeyer 1974), but 

seed longevity in the field is unknown 

(Young and Young 1992). Plants can 

flower and set seed within 3 years 

following germination (Borell 1962). 

Vegetative spread can also occur as 

numerous root suckers are produced 

at the root crown after a disturbance 

to the shoot system.

Riparian is a word 

used to describe 

anything connected 

with or next to the 

banks of a stream, 

pond, or lake. A 

“riparian area” is a 

body of water and 

the land adjacent to 

it. Riparian areas 

typically have a 

unique combination 

of fl ora, fauna, and 

soil characteristics 

compared to nearby 

deserts, grasslands, 

or forests. Although 

riparian areas 

occupy less than 

one percent of the 

landscape, they 

support some of the 

greatest diversity 

of plant and animal 

species and are 

essential habitat for 

much of the native 

Southwestern fl ora 

and fauna.
6 Strategy for Long-term Mgmt. of Exotic Trees in New Mexico’s Riparian Areas

Siberian elm (Ulmus pumila):

Siberian elm is a deciduous tree that 

can reach over 70 feet in height. It 

is native to northern China, eastern 

Siberia, Manchuria, and Korea. The 

species was introduced into the 

United States in the 1860s as an 

ornamental tree. Siberian elm has 

escaped cultivation and is currently 

established throughout the central 

and southwestern United States. 

This plant is typically found along 

riparian areas, but it has been 

observed to invade roadsides, 

meadows, and upland areas. 

Infestations are present in the upper 

reaches of the Rio Grande, Pecos 

River, and other river systems, and 

are spreading into higher elevations.

Siberian elm flowers from 

February through April in New 

Mexico depending upon elevation, 

temperature, and precipitation 

patterns. It is often erroneously 

identified as Chinese elm (Ulmus 

parvifolia), an autumn-flowering 

species. Siberian elms produce 

many winged fruit, each of which 

contains one seed. Seeds are 

spread by wind and can produce 

blankets of seedlings in areas void of 

vegetation. Seeds readily germinate 

and seedlings grow rapidly and 

compete with resident vegetation. 

Densities as high as 4,200 seedlings 

per acre have been observed (Jim 

Brooks, Ciudad SWCD, personal 

communication). It is not known 

how long seeds remain viable. Rapid 

and prolific resprouting can occur 

when the shoot system is disturbed, 

causing local vegetative spread.

Water Basins Not Currently 

Considered: Although closed basins 

are not addressed in this plan, 

exotic trees are considered to be 

a significant problem in the Little 

Colorado, Central Closed, Tularosa 

and Hueco, Salt, Southwest 

Figure 4. Siberian elm leaves.

Figure 5. Saltcedar plant has formed sand pedestal in White Sands National 

Monument, National Park Service. 
Strategy for Long-term Mgmt. of Exotic Trees in New Mexico’s Riparian Areas 7

Draft

Table 2. Summary of Environmental Impacts of Exotic Tree Species in 

New Mexico1

Species Hydrology

Fire 

Frequency Soil Salinity

Community 

Diversity

Salt-cedar Stabilizes 

streambank 

edges 

leading to 

channelization 

of stream (Graf 

1978).

Saltcedar 

evapotranspiration rates 

exceed that 

of native 

replacement 

vegetation 

in many 

circumstances 

(King and 

Bawazir 2000, 

Dahm et al. 

2002).

Fire adapted 

species 

that rapidly 

resprouts 

after fi res, 

and recovers 

faster than 

native species 

(Busch and 

Smith 1995).

Increased fi re 

frequency of 

infested areas 

has been 

observed.

Plants take 

up salt from 

the soil, 

store it in the 

leaves, and 

then release 

it into the 

environment. 

Saltcedar is 

adapted to a 

wide range of 

salinity levels 

(Shafroth 

1995).

Dense 

stands have 

low native 

woody and 

herbaceous 

plant diversity 

(Campbell and 

Dick-Peddie 

1964).

Interferes with 

regeneration 

of woody 

perennials 

such as 

cottonwoods 

(Taylor et al. 

1999).

Reduced avian 

diversity (Ellis 

1995), reduced 

herpetofauna 

(Konkle 1996).

Russian 

olive

Alters nutrient 

cycling (Howe 

and Knopf 

1991).

Can also 

stabilize 

streambank 

edges, 

leading to 

channelization 

of stream.

Believed to 

be a large 

consumer 

of water, but 

no data is 

available.

No information 

available on 

fi re frequency, 

but it rapidly 

resprouts after 

fi res.

Salt tolerant 

compared 

with other 

species 

(Monk and 

Wiebe 1961).

Dense stands 

have reduced 

biodiversity 

(Waring and 

Tremble 1993).

Siberian 

elm

Could be 

a large 

consumer of 

water, but no 

data available.

No information 

available on 

fi re frequency, 

but it rapidly 

resprouts after 

fi res.

No data is 

available.

No data is 

available.

1

 Many of these processes are density and age dependent, with dense old infestations 

showing the largest changes in the ecosystem.

Locally, the 

Spanish term 

“bosque” is 

commonly 

used to 

refer to the 

woodland 

fringe along 

river systems.
8 Strategy for Long-term Mgmt. of Exotic Trees in New Mexico’s Riparian Areas

Closed, and Southern High Plains 

Basins. The management concepts 

addressed in this strategy can be 

applied in these closed basins.

Overview of Integrated 

Vegetation Management 

(IVW) Approach

Cooperating agencies, organizations, 

and individual landowners must 

have a shared long-term vision 

for management of exotic riparian 

species in the river systems in New 

Mexico to accomplish long-term 

control. Several effective strategic 

guides to weed management have 

been developed. They emphasize 

prevention, early detection and 

mapping, timely control, and 

adaptive management (Pulling 

Together, National Strategy for 

Invasive Plant Management, multiagency support organization; 

Partners Against Weeds, Bureau 

of Land Management, 1996; and 

Stemming the Invasive Tide, 

Forest Service Strategy for Noxious 

and Nonnative Invasive Plant 

Management, 1998). This strategy 

addresses each of these elements.

Elements 

of the Strategy

Management actions can be 

optimized by adopting a systematic 

approach, such as IVM. This 

strategy emphasizes IVM 

methodology including prevention, 

containment, and control of exotic 

species. These concepts have been 

successfully implemented by many 

groups for control of other weeds in 

the West.

A long-term management strategy 

in the selected river systems must 

address all types of riparian areas: 

(1) those not yet infested; (2) those 

with light infestations; (3) areas with 

special considerations; and (4) areas 

of extensive infestation. At the same 

time, the strategy must be designed 

to result in a progressive reduction of 

overall infestation levels. Each river 

system needs to be addressed as a 

whole.

Management objectives will vary 

based on the level of infestation and 

the location of a site within the river 

system (Taylor and McDaniel 2004). 

All management efforts should 

contribute to the overall reduction 

of infestation levels. It is important 

to note that implementation of this 

strategy does not preclude local 

managers from initiating projects to 

achieve local objectives, although 

policy makers must understand 

that management of infestations 

at the top of the watershed will 

improve sustainability of programs 

downstream. The following are 

varying levels of infestation within a 

river system and priorities for their 

management: 

• Uninfested Headwaters and 

Other Sites: The priority is 

to protect these sites from 

infestation, prevent upstream 

seed sources, and maintain or 

improve the health of existing 

native plant communities.

• Riparian Sites with Light 

Infestations: The priority is 

to remove exotic trees, reduce 

upstream seed sources, and 

protect and enhance existing 

native plant communities.

• Areas of Special Concern: The 

priority is to identify riparian 

areas or wetlands that have 

a special focus (recreational 

uses or critical habitat for 

threatened, endangered, 

or sensitive species) and to 

preserve, create, or enhance the 

unique attributes on such sites.

• Densely Infested Sites: The 

priority is to remove dense or 

monotypic stands of exotic 

trees and restore desirable 

plant species to achieve specific 

objectives.
Strategy for Long-term Mgmt. of Exotic Trees in New Mexico’s Riparian Areas 9

Draft

Headwaters and Other Uninfested 

Sites: Preventing new infestations 

from forming is extremely important 

as it helps to maintain desirable 

plant community structure and 

function. Prevention includes 

limiting dispersal of seeds and plant 

parts from nearby areas, minimizing 

soil disturbance, and maintaining 

or improving the health of 

competitive plant species. Generally, 

regeneration will not be required if 

natural processes enable desirable 

plant maintenance and recruitment.

Riparian sites that have not yet 

been infested by exotic trees and 

have relatively healthy native and 

desirable plant communities need to 

be conserved. Invasion of riparian 

sites can be a slow process and 

healthy native plant communities 

can generally offer competition 

to invasion by exotic trees (Sher 

et al. 2002). Although a detailed 

inventory of the five river systems 

has not been conducted, many 

uninfested areas are present in 

the upper reaches of drainages, 

especially for the Rio Grande, Pecos, 

and Gila/San Francisco Rivers. 

Periodic surveillance of these sites 

will need to be done and exotic trees 

discovered during surveys will need 

to be immediately removed.

Riparian Sites With Light 

Infestations: Riparian areas with 

relatively light infestations and 

relatively healthy native plant 

communities usually can be 

treated and restored economically. 

Early detection will also minimize 

management costs and negative 

impacts these exotic trees impose 

on the system. Per acre costs for 

control increase as densities of 

exotic trees increase. The main 

economic advantage to early 

treatment of these areas is avoiding 

costly restoration efforts.

Surveys are needed to inventory the 

location and size of infestations as 

well as other plant species present 

within the area. Ideally, surveys 

should be done annually to allow 

for detection of new infestations 

and allow for prompt management. 

Areas with a high risk of infestation 

may need to be surveyed more 

frequently to ensure early detection. 

Information can be mapped, which 

will aid in establishing priorities 

and developing or adjusting local 

management.

Once an area is mapped, goals need 

to be established for management 

of individual infestations to provide 

for sustainable, long-term control 

through regeneration (Taylor and 

McDaniel 2004). These goals should 

be specific and have measurable 

outcomes that are realistic. 

Prioritization of programs based on 

the level of infestation and potential 

for natural restoration will optimize 

the area to be treated with existing 

resources.

Since water dispersal of seeds 

is significant for saltcedar and 

Siberian elm, treatments, whenever 

possible, should begin at the upper 

reaches of a drainage and progress 

downstream. Treatment of Russian 

olive infestations is similar, but the 

long-range dispersal of seed by birds 

reduces the effectiveness of the 

watershed approach. 

Treating Areas of Special Concern:

Special areas of concern include the 

following: (1) habitat for threatened, 

endangered, and sensitive species; 

(2) dense stands of saltcedar and 

riparian sites with heavy fuel 

accumulations that increase the risk 

of wildfire; (3) historical cottonwood 

gallery forests; (4) areas of religious 

and cultural significance; and (5) 

areas where perennial water could 

be restored.

Treatment methods for such sites 

should be based on management 

objectives and existing conditions. 

As with areas with light infestations, 

selective methods would be most 

appropriate where a remnant 

of native or desirable plants is 

present. However, some sites may 

need extensive tree removal and 

Invasive plants 

are considered 

naturalized 

when they have 

adapted to local 

conditions and 

have the ability 

to reproduce 

and establish 

more readily 

since initial 

introduction.
10 Strategy for Long-term Mgmt. of Exotic Trees in New Mexico’s Riparian Areas

restoration to achieve specific 

objectives, and involve a variety of 

control methods.

Presently, the species of concern 

most closely associated with 

management of exotic trees in New 

Mexico include the endangered 

Southwestern willow flycatcher (Empidonax trailii extimus) and 

the yellow-billed cuckoo (Coccyzus 

americanus). The designation of 

critical habitat for the endangered 

Southwestern willow flycatcher is 

scheduled for completion by the 

U.S. Fish and Wildlife Service in late 

2005, while the yellow-billed cuckoo 

is being considered for listing as a 

threatened species (April Fletcher, 

U.S. Fish and Wildlife Service, 2003, 

personal communication). Within 

these areas, specific treatments 

can be designed to maintain and 

improve vegetative conditions for 

these species by applying selective 

exotic tree removal within breeding 

areas. Treatments could occur in 

the fall or winter outside of the 

breeding season.

Treating Monotypic Stands: Large 

reaches of the Rio Grande, Pecos, 

Canadian, San Juan, and Gila River 

systems currently have monotypic 

stands of saltcedar and Russian 

olive with only a few remnants of 

native plant communities. Russian 

olive and Siberian elm appear to be 

more abundant at higher elevations, 

especially in the northern parts of 

the State. Without intervention, 

an increasingly larger area will be 

permanently modified by these 

exotic tree infestations. Eradication 

is an unrealistic objective for 

such large, dense infestations. 

Containment and annual density 

reduction is more practical.

Russian olive infestations can 

develop under dense stands 

of saltcedar and could become 

more dominant in some riparian 

areas. Removal of one species 

would provide an opportunity for 

the spread and intensification of 

the other species, including the 

potential for invasion by herbaceous 

exotics. Rapid revegetation following 

control can provide competition 

against such invasions and lead to 

lasting, sustainable control that is 

resistant to invasion (Taylor and 

McDaniel 2004).

Control of dense infestations is 

often done for a variety of objectives. 

Monotypic stands of saltcedar are 

at high risk from wildfire, which 

is of particular concern to nearby 

residential communities (Taylor 

2000). In some instances, saltcedar 

can alter ground water hydrology 

as water tables decline and sites 

become more xeric (dry) (Lovich 

et al. 1994). Control of large, 

monotypic stands may increase 

water in some areas (King and 

Bawazir 2000, Dahm et al. 2002).

Management 

Techniques

Several methods have been shown 

to be effective in managing exotic 

trees. Selection of the appropriate 

methods depends on a number 

of factors, such as infestation 

density, management objectives, 

environmental concerns, costs, 

and social considerations. 

Restoration potential also is an 

important consideration. No 

method will provide 100 percent 

control and followup treatments 

will be needed for many years to 

achieve desired results. As new 

techniques could become available 

during implementation of this 

strategy, decision makers will need 

to exercise managerial flexibility 

to adopt these new methods. An 

example of this could be the use of 

biological control agents.
Strategy for Long-term Mgmt. of Exotic Trees in New Mexico’s Riparian Areas 11

Draft

Table 3. Estimated cost per acre and expected percent of control 

for individual saltcedar treatments and large scale control 

methods (adapted from Taylor and McDaniel 2004)

Control Treatment Cost per Acre

Percent 

Control

Individual Plant Treatments

Manual Removal (Immature Plants) 0-$5,000 95-100

Mechanical Grubbing $40-$300 97-99

Low-volume Herbicide Application1 $30-$60 80-95

Cut-stump Herbicide Application2 $1,600-$2,5006 60-80

Ground-based Foliar Herbicide $40-$300 97-99

Large Scale Control

Mechanical $700 97-99

Airplane Herbicide-Burn $300 93

Helicopter Herbicide-Burn4 $240 89

Airplane Herbicide-Shred3,5 $400 97-99

Helicopter Herbicide-Shred4 $510 97-99

Airplane Herbicide-Burn-Mechanical $380 97-99

Helicopter Herbicide-Burn-Mechanical4 $490 97-99

1 Doug Parker, 2003, personal communication

2Duncan 2003

3McDaniel and Taylor 2003a

4McDaniel and Taylor 2003b

5Includes 2 years of followup, ground-based foliar herbicide treatment

6The majority of the cost will be for tree cutting and removal or chipping, and the 

herbicide cost can vary from $20-$60 per acre.

Light Infestations 

and Areas of Special 

Concern

• Manual Removal: Immature 

plants (about 2 feet tall or 

less) can often be controlled by 

hand-pulling or grubbing. To 

be effective, most of the root 

structure must be removed 

and destroyed. Saltcedar, 

Russian olive, and Siberian 

elm can readily reproduce 

from cut stems and sections of 

buried roots. Improper removal 

and disposal can result in 

vigorous regrowth. Unless 

performed by volunteers, the 

cost for manual removal of 

dense thickets of seedlings can 

be prohibitively expensive.

• Selective Mechanical 

Grubbing: Mechanical 

grubbing can selectively 

remove individual trees on 

sites that have good access 

(Taylor and McDaniel 2004). 

To be effective, the complete 

root system must be excavated 

and removed from the site. 

Mechanical removal can result 

in soil disturbance causing 

impacts to resident vegetation, 

but soil disturbance may be 

necessary on some sites to 

restore desired vegetation 

(Taylor and McDaniel 2003). 

A 

phreatophyte 

is a deeprooted plant 

that occurs 

along rivers 

or other wet 

sites and 

obtains its 

water from 

the water 

table.
12 Strategy for Long-term Mgmt. of Exotic Trees in New Mexico’s Riparian Areas

although fall through spring 

applications are preferred. 

Adverse effects to desirable 

plants can be avoided when 

they are dormant. This is 

a cost effective method for 

selective control of small 

diameter trees (Table 3). 

Triclopyr will have little or no 

effect on grasses and desirable 

trees and shrubs will not 

be affected unless directly 

sprayed.

• Cut-stump Herbicide 

Application: For large trees 

with thick bark, a low-volume, 

cut stump method involves 

a combination of cutting 

and herbicidal treatment 

to achieve “root kill.” This 

involves cutting the trunk 

just above the ground and 

immediately applying an amine 

or ester formulation (mixed 

with vegetable oil) of triclopyr 

(Parker and Williamson 2003) 

or imazapyr to the cut surface 

(Duncan 2003). Cutting large 

Figure 6. Selective control of Russian olive and saltcedar saplings following basal bark 

application.

The initial cost to purchase 

equipment for mechanical 

removal is high, and annual 

maintenance costs will 

be required. Equipment 

contracting can be a more 

economical approach for using 

mechanical methods. See 

Table 3 for cost estimates.

• Low-volume Basal Bark 

Herbicide Application: Small 

saltcedar, Russian olive, and 

Siberian elm saplings and 

regrowth (stems less than 2-3 

inches in diameter at ground 

level and less than 8 feet 

tall) can be controlled by a 

basal application of triclopyr 

(ester formulation) mixed with 

vegetable oil or another proven 

carrier. This technique involves 

the selective application of a 

herbicide to control individual 

plants or groups of plants 

using backpack sprayers 

(Parker and Williamson 

2003). Applications can be 

done at any time of the year, 
Strategy for Long-term Mgmt. of Exotic Trees in New Mexico’s Riparian Areas 13

Draft

trees with chain saws can be 

dangerous, but this approach 

is a cost effective, selective 

treatment for light infestations. 

Per acre costs depend on tree 

density, and the majority of 

the cost is for tree cutting and 

removal or chipping of the 

woody debris.

• Foliar Herbicide Application:

Foliar applications of a mixture 

of imazapyr and glyphosate 

are effective when applied 

between June and September. 

The addition of a nonionic 

surfactant to the spray mix is 

recommended. Glyphosate has 

been shown to be effective in 

controlling Russian olive when 

applied in June (McDaniel et 

al. 2002), but the application 

of imazapyr in August and 

September, when trees are 

moving carbohydrate reserves 

to their root systems, is 

more effective (Duncan and 

McDaniel 1998, Duncan 2003). 

Complete foliar coverage of 

individual plants is necessary, 

and care must be taken to 

not adversely affect adjacent 

desirable vegetation. Imazapyr 

and glyphosate are considered 

broad spectrum herbicides and 

will injure or kill plants that 

intercept the spray solution. 

This can be a cost effective 

method where infestations 

are accessible with backpack 

sprayers or ATV mounted 

spray equipment. Costs are 

density dependant and can 

be high due to the volume of 

herbicide solution that must 

be applied to obtain complete 

coverage of the foliage (Table 

3). Imazapyr does not control 

Siberian elm.

Densely Infested Sites

• Mechanical Removal: For 

dense monotypic stands, trunk 

and stem removal by heavy 

machinery followed by root 

plowing and raking can be an 

effective method (McDaniel and 

Taylor 2003a, 2003b). This 

technique is appropriate where 

there is no concern about 

affecting associated desirable 

plants. Trunks and stems 

should be cleared during the 

winter to avoid over heating 

equipment, while root plowing 

and raking should occur 

during hot summer months to 

aid in desiccation of roots. As 

with other control programs, 

followup control will be 

required until plant densities 

are reduced to acceptable 

levels. Large scale clearing 

may require revegetation 

Figure 7. Cut-stump hand application of 

triclopyr (amine formulation) immediately 

following cutting of saltcedar stems with 

a chain saw.

Treatment 

of exotic tree 

infestations 

must be 

coordinated 

throughout 

an entire river 

system to 

ensure New 

Mexico’s 

nonnative 

phreatophyte 

program is 

successful and 

sustainable.
14 Strategy for Long-term Mgmt. of Exotic Trees in New Mexico’s Riparian Areas

to discourage reinfestation 

or invasion by other exotic 

species (Taylor and McDaniel 

2004). Control and restoration 

costs can be very high (Table 

3).

• Aerial Herbicide 

Applications: Large, dense 

infestations also can be 

controlled through the aerial 

applications of imazapyr 

or a mixture of imazapyr 

and glyphosate. A nonionic 

surfactant is recommended for 

both applications. Applications 

must occur from late August 

through September prior to 

color change when plants are 

actively growing (Duncan and 

McDaniel 1998, McDaniel 

and Taylor 2003a, 2003b). 

The use of fixed wing aircraft 

can be more economical when 

treating large saltcedar blocks, 

while the use of a helicopter is 

more appropriate for precision 

application around water 

bodies and desirable vegetation 

(McDaniel and Taylor 2003b). 

These herbicides are slow 

acting and treated trees 

should not be removed for a 

period of 3 years to achieve 

desired “root kill”. As with 

other treatments, followup 

control will be required until 

plant densities are reduced 

to acceptable levels. As with 

large scale mechanical control 

programs, revegetation may 

be required for sustainable, 

long-term control. Control and 

restoration costs can be high 

(Tables 3 and 5).

• Combination of Control 

Methods: Frequently large 

scale mechanical and aerial 

herbicide treatments can be 

combined with burning or 

debris shredding to reduce 

costs and prepare sites for 

either natural regeneration 

or artificial regeneration 

(Taylor and McDaniel 

2004). Regardless of control 

techniques used, costs are 

high for treating large exotic 

monocultures. Considering 

restoration requirements 

for sustained, long-term 

control, sites designated 

for plant removal should 

be prioritized based on 

regeneration potential prior to 

Figure 8. Root plowing of saltcedar on Bosque del Apache National Wildlife Refuge.
Strategy for Long-term Mgmt. of Exotic Trees in New Mexico’s Riparian Areas 15

Draft

initiating control programs. 

Insight into appropriate 

exotic vegetation control 

strategies is also obtained 

when the mechanisms for site 

restoration are considered.

Restoration

Natural regeneration and artificial 

planting are intended to return sites 

to plant communities dominated 

by native or desirable species. 

Desirable vegetation can protect 

and enhance hydrologic functions, 

increase wildlife habitat, and 

discourage reinvasion of nonnative 

species.

An example of natural herbaceous 

regeneration is on the Pecos River, 

where there is a connection between 

high ground and surface water, 

which resulted in the regeneration 

of saltgrass (Distichlis stricta) and 

alkali sacaton (Sporobolus airoides) 

following saltcedar removal (Walthall 

2004). Natural woody regeneration 

by cottonwoods and willows occurs 

Figure 9. Use of prescribed fire to remove saltcedar woody debris following aerial 

herbicide treatment, Bosque del Apache National Wildlife Refuge.

on the Rio Grande where groundsurface water connectivity are high 

and where appropriate flooding 

still occurs following saltcedar 

removal (Taylor et al. 1999, Taylor 

and McDaniel 2003). In the first 

case, aerial herbicide application 

combined with burning may be 

sufficient for natural regeneration 

to occur, while in the second case 

a combination of techniques which 

include mechanical soil scarification 

are required.

Where ground and surface water 

connectivity is low and/or flooding 

no longer occurs, artificial planting 

or seeding may be required to 

establish vegetation able to compete 

with exotic re-infestation or 

invasions by other exotic species. 

Artificial regeneration prescriptions 

are extremely rigid and are based 

primarily on soil type, depth to 

water table, and soil salinity (Taylor 

and McDaniel 2003). See Tables 4 

and 5 for information on current 

techniques and cost associated with 

various options.

Effectiveness, 

cost, restoration 

potential, and 

the risk of 

causing adverse 

environmental 

impacts are 

important 

considerations 

when 

determining 

which sections 

of a river 

system to treat.
16 Strategy for Long-term Mgmt. of Exotic Trees in New Mexico’s Riparian Areas

Revegetation Technique Cost Per Acre

Pole Planting1 $900

Tallpot Containerized Stock1 $2,700

Rainfall Harvest2 $7,200

Seeding3 $120

1 100 per acre

2 100 foot rows with 3 foot plant spacing and 15 rainfall harvest rows per acre.

3 Seeded with an Australian pitter seeder at the rate of 13.6 pounds per acre for 

saltbush and 1.5 pounds per acre alkali sacaton.

Table 4. Description of restoration and rehabilitation used successfully 

in New Mexico (adapted from Taylor and McDaniel 2004a)

Method Timing Effectiveness Comments

Controlled flooding: Flood 

areas when seeds from 

desirable species are 

present. 

When native 

or desirable 

seeds are 

available on 

site.

Cottonwood and 

willow survival 

20% to 47% 

after 2 years.

Continuing 

control of 

invasive exotics 

is critical.

Pole plantings: Cutting 

and planting stems of 

willows and cottonwoods 

from established trees. 

Butt ends are soaked in 

water 10 days prior to 

planting into water table 

(Taylor and McDaniel 

1998).

During winter 

months: 

January 

through 

March in New 

Mexico. 

Plant survival 

90%

For wildlife 

benefit, density 

should be at 

least 100 trees 

and shrubs per 

acre.

Nursery stock: Place 

understory plants with at 

least 30 cm of roots into 

holes that are augered to 

the water table (Dreesen 

et al. 2003). 

Planting: 

August best, 

but requires 

supplemental 

water for 1-2 

months.

Plant survival 

90%

Survival 

decreases if 

water table is 

greater than 5 

feet. Density 

should be at 

least 100 trees 

or shrubs per 

acre to benefit 

wildlife.

Rainfall harvest: 

Construct a long 

shallow V-shaped water 

catchment furrow and 

line the sides with plastic. 

Seedlings are planted 

at 5 foot intervals at the 

bottom of the catchment 

(Fenchel et al. 1996).

Construction: 

Before rains

Planting: 

During 

monsoon 

season.

Results are 

comparable 

to previous 

methods.

Effective in areas 

with a deep 

water table or 

where moderate 

salinity levels are 

present in the 

soil.

Table 5. Revegetation techniques and costs on the Bosque del Apache 

National Wildlife Refuge, New Mexico (Adapted from Taylor 

and McDaniel 2004)
Strategy for Long-term Mgmt. of Exotic Trees in New Mexico’s Riparian Areas 17

Draft

Program Requirements

Comprehensive Inventory:

Although we have broad summaries 

of the plant communities and 

levels of exotic tree infestations 

found in riparian areas (Muldavin 

et al. 2000), more comprehensive 

surveys are needed on each river 

system. We need more precise 

information on the extent and 

intensity of infestations and the 

location and condition of native 

plant communities. Only with this 

baseline information will we be able 

to adequately determine the success 

of treatments.

A complete and detailed inventory 

of the five river systems and 

baseline vegetation maps will 

establish current infestation levels 

for saltcedar, Russian olive, and 

Siberian elm, and the location of 

existing stands of native trees and 

other native plant communities. 

This information is needed to 

determine where to implement 

projects in the various priority 

areas. An inventory will provide 

baseline information necessary to 

determine the success of treatments 

to reduce infestations of the exotic 

tree species and protection and 

restoration of stands of native trees, 

shrubs, and other plants.

A specific implementation plan will 

be developed by the New Mexico 

Interagency Weed Action Group 

that outlines methods and costs to 

conduct an inventory for each of the 

five river systems in New Mexico. A 

comprehensive inventory of all river 

systems could take at least 2 years 

to complete and could cost as much 

as $1,000,000 to $1,500,000.

Long-term Funding: Adequate, 

consistent, and long-term funding 

is needed to prevent the continued 

spread of exotic tree infestations, 

control existing infestations, and 

maintain or restore native plant 

communities along the five major 

river systems in New Mexico. It 

must be emphasized that some 

treatment and restoration programs 

have been successfully implemented 

in New Mexico, such as on the 

Bosque del Apache National Wildlife 

Refuge, where about 2,000 acres 

have been restored since 1987. 

These efforts, however, have only 

addressed a small percentage of 

the overall problem. To accomplish 

the objectives outlined in this 

strategic plan, it is estimated that 

at least $64,400,000 of Federal 

and State cost-share funding 

(including volunteer and in-kind 

services) will be needed over a 

10-year period to make significant 

progress in protecting and restoring 

riparian areas in the State (Table 

6). This is the best estimate that 

can be developed at this time, 

especially since we do not know 

the extent of infestations. As better 

information becomes available 

through inventories and annual 

measurements of success, we will 

be able to adjust annual budgets 

to achieve desired control and 

restoration objectives for the five 

river systems. At this time, we can 

only estimate the minimal threshold 

for annual funding that would be 

needed to be successful. It must be 

understood that inadequate funding 

may not produce any significant 

control, and the long-term result 

may not be any different than 

taking no action. As an example, the 

overall acreage of saltcedar, Russian 

olive, and Siberian elm infestations 

may increase by as much as 3 to 

7 percent annually. Assuming a 

total infestation level of 500,000 

acres, which may be a conservative 

estimate, the existing infestations 

could increase and intensify on 

152,400 to 419,200 acres over the 

next 10 years (Figure 10).

Technical Support Organization:

To successfully coordinate treatment 

and restoration programs over the 

long-term and promote proper and 

safe implementation of treatments, 

it will be necessary to build a strong 

team of technical specialists (three 

or more permanent employees) 

Regeneration 

refers to natural 

herbaceous 

or woody 

revegetation of 

disturbed sites 

by native species 

where surface 

and ground water 

connectivity 

is high and 

natural fl ooding 

processes still 

occur (Molles 

et al. 1998, 

Taylor et al. 

1999, Stromberg 

1997, Taylor and 

McDaniel 2003).
18 Strategy for Long-term Mgmt. of Exotic Trees in New Mexico’s Riparian Areas

who have the sole responsibility 

of providing technical advice and 

assistance to local managers to help 

ensure the quality, consistency, and 

continuity of programs. Success 

for such a technically complex 

and long-term program is always 

derived from technically competent 

people working cooperatively 

with local managers. In addition, 

these specialists would provide 

technical information to local 

managers and participate in 

inventory, detection, education and 

information, demonstrations and 

research, control, and restoration 

efforts. The initial cost to support 

this organization would be about 

$300,000 per year and increase over 

time due to inflation.

Education and Information: Two 

separate information and education 

programs are needed. First, Federal, 

State, and local officials; tribal 

leaders; and private landowners 

will need training in prevention, 

suppression, and restoration 

techniques. Due to turnover of 

Table 6. Estimated annual funding (thousands of dollars) needed to 

accomplish the strategic objectives

Fiscal 

Year

Technical 

Support 

OrganizationInventory/ 

Monitoring

Education/ 

Information

Research/

Demonstration/Pilot 

Projects

Control/

Restoration

Total 

Annual 

Cost

2005 300 750 50 500 2,000 3,600

2006 300 750 50 750 4,000 5,850

2007 300 200 50 1,000 6,000 7,550

2008 300 50 50 1,000 6,000 7,400

2009 350 50 50 500 6,000 6,950

2010 350 50 50 300 6,000 6,750

2011 350 50 50 100 6,000 6,550

2012 350 50 50 100 6,000 6,550

2013 400 50 50 100 6,000 6,600

2014 400 50 50 100 6,000 6,600

Total 3,400 2,050 500 4,450 54,000 64,400

Percent 5 3 1 7 84 100 Acres

2004 2005 2006 2007 2008 2009 2010 2011 2012 2013

450,000

500,000

550,000

600,000

650,000

700,000

750,000

800,000

850,000

900,000

950,000

3%

5%

7%

Year

Figure 10. Potential for acreage increase of 

saltcedar, Russian olive, and Siberian elm 

infestations assuming an initial infestation 

level of 500,000 acres and annual rates of 

increase of 3, 5, and 7 percent.
Strategy for Long-term Mgmt. of Exotic Trees in New Mexico’s Riparian Areas 19

Draft

the people, this activity would 

need to be done on a continuing 

basis. Second, development and 

implementation of outreach 

programs are needed to inform the 

public of the seriousness of the 

threat to riparian areas, and the 

consequences of failure to control 

the exotic tree infestations. The 

technical support organization could 

accomplish a major portion of an 

education effort, but providing an 

additional $50,000 per year would 

optimize success.

Measuring Success: Annual 

assessments are needed for 

treatment and restoration programs. 

Measurements should be tailored 

to evaluate if the specific objectives 

for a site were met. For example, if 

the objectives are to increase water 

availability, enhance wildlife habitat, 

and reduce wildfire risk, managers 

will need to establish three specific 

assessment measurements and 

conduct pre- and post-monitoring 

to determine if the objectives are 

met. Written monitoring plans 

should be prepared before beginning 

treatments.

Demonstrations: Three types of 

demonstration areas are needed: (1) 

sites to show successful control and 

restoration methods; (2) sites for 

training landowners and managers 

in the application of IVM techniques; 

and (3) sites to evaluate new and 

innovative methods of control. 

These sites will be used to increase 

awareness of both land managers 

and the general public.

Research: While some progress has 

been made in developing successful 

techniques for removal of exotic 

trees, site restoration, and for 

evaluating water use by native and 

nonnative species, many questions 

remain (Dr. James Gosz, University 

of New Mexico, 2003, personal 

communication). Quantifying the 

hydrologic response to exotic tree 

management is one of the more 

important research topics. To 

understand this influence, we will 

need to understand the general 

influences of the hydrological cycle 

throughout a given water basin in 

addition to any specific research 

on exotic tree control methods. 

There are large uncertainties with 

current estimates, especially for 

evapotranspiration and surface/

ground water interactions. The 

key will be to determine if longterm exotic tree removal and 

restoration efforts will increase 

water availability. In addition, 

key research efforts are needed to 

determine; (1) physiological biology 

of exotics; (2) reproductive biology of 

exotics under varying environmental 

conditions; (3) assessment of the 

seed sources and seed dispersal 

leading to new establishments; 

(4) identification and use of nonnative biological control agents; 

(5) potential of native plant 

communities to offer competition to 

exotics; and (6) controlled flooding 

management effects on native and 

nonnative species and ecosystems. 

A separate plan will be developed to 

identify key research needs.

Pilot Projects: Currently several 

projects are underway which may 

result in additional control options. 

The saltcedar leaf beetle (Diorhabda 

elongata) shows considerable 

promise as a future biological 

control agent (Lewis et al. 2003). In 

2003, the Crete strain of this beetle 

was released on a site on the Pecos 

River near Artesia, New Mexico, 

and its spread and affects on 

saltcedar will be closely monitored 

(Dr. David Thompson, New 

Mexico State University, personal 

communication). In addition, New 

Mexico’s legislature has funded 

research to evaluate the effects of 

grazing by goats on saltcedar and 

other exotic trees (New Mexico SB 

655, 2003).
20 Strategy for Long-term Mgmt. of Exotic Trees in New Mexico’s Riparian Areas

Ornamental Trees in Residential 

Communities: The presence 

of saltcedar, Russian olive, and 

Siberian elm trees in communities 

and other lands adjacent to riparian 

areas cannot be ignored. Seed 

produced by ornamental trees will 

continue to re-infest riparian areas. 

Incentives for removal of these 

species, and restrictions on their 

sale, will have to be addressed, 

otherwise, re-infestation of riparian 

sites will occur and long term and 

sustainable control is unlikely.

Compliance with Laws and 

Regulations: For Federal lands 

or where Federal funds will be 

used, compliance with the National 

Environmental Policy Act (NEPA) 

is usually required. To expedite 

project implementation, it will be 

worthwhile for agencies to develop 

a programmatic environmental 

analysis for the river systems in 

New Mexico. Prior to implementing 

management programs, consultation 

with the U.S. Fish and Wildlife 

Service is required to avoid negative 

impacts on the Southwestern 

Willow Flycatcher and its habitat or 

other species of concern. For some 

projects it may also be necessary to 

obtain Federal, State, and or local 

permits of varying types (e.g., burn 

permits). 

Conclusions

While many factors must be 

considered when developing a local 

management plan for exotic tree 

species, it is important to develop 

a plan that will enable long-term 

management that is adaptable to 

meet the specific objectives of each 

area. Management plans should 

include mapping, prevention, early 

detection, timely control, and 

adaptive management of infested 

areas, including regeneration. 

Linking management plans over 

entire river basins, prioritizing 

areas, and spending resources 

efficiently can contain the spread 

of exotic tree infestations, reduce 

overall infestation levels, and lead 

to more diverse riparian ecosystems 

that are healthy and sustainable.

The use of trade or fi rm 

names in this publication is 

for reader information and 

does not imply endorsement 

by the U.S. Department of 

Agriculture of any product or 

service.
Strategy for Long-term Mgmt. of Exotic Trees in New Mexico’s Riparian Areas 21

Draft

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Figure 11. Natural regeneration of cottonwood seedlings on sandy flat of Rio Grande, 

Overbank Demonstration Project.
24 Strategy for Long-term Mgmt. of Exotic Trees in New Mexico’s Riparian Areas